The present invention relates to a position measuring system for measuring a position such as a working position based on photodetecting condition of a laser beam by projecting the laser beam in rotary irradiation and by receiving the laser beam reflected by an object.
In the past, as a representative system for forming a reference plane by projecting a laser beam in rotary irradiation, a rotary laser system and a photodetection system for receiving the laser beam have been known.
The rotary laser system is designed to form a reference plane by projecting a laser beam with luminous flux in spot-like shape. For instance, by projecting the laser beam within a horizontal plane by rotary irradiation, a horizontal reference plane is formed. By projecting the laser beam within a vertical plane by rotary irradiation, a vertical reference plane is formed. By projecting the beam within a tilted plane by rotary irradiation, a tilted reference plane is formed.
The photodetection system comprises a photodetection unit for receiving and detecting a laser beam. Based on the laser beam detected by the photodetection unit, a horizontal reference position, a vertical reference position, etc. are determined. The rotary laser system and the photodetection system can make up together a position measuring system. The position measuring system utilizing a reference plane formed by the laser beam is effective for the use in civil engineering work, which is carried out for a wide range of operation.
In case the position measuring system is used for wide range of outdoor operation as in the case of civil engineering work using construction machines, a reference plane is detected by the photodetection system installed on the construction machine. Based on the reference plane thus detected, a working position of the construction machine is measured. In this case, positioning range of the photodetection system with respect to the reference plane is also wider. When the photodetection unit is small, an operator has difficulty to perform manual operation, and the photodetection unit of larger size is used. For instance, in case the reference plane formed is a horizontal reference plane, the photodetection system sometimes has a photodetection unit of several tens of centimeters—sometimes more than 1 meter—in a vertical direction.
When a construction machine, which is represented by a bulldozer, is used, management of working on a plane is carried out by a combination of a rotary laser system and a photodetection system installed on the construction machine. When working condition of the construction machine is to be controlled, a GPS position measuring unit is added to this combination. Such system is operated for 3-dimensional working control including positions on the ground surface and a height. The position in a horizontal direction on the ground surface is detected by the GPS position measuring unit. For the detection of the position in the direction of height, the rotary laser system and the photodetection system are used for stabilizing purposes.
FIG. 8 shows a conventional type working position measuring system when a photodetection system is installed on a construction machine.
In the figure, reference numeral 1 denotes a rotary laser system, and 2 denotes a construction machine (a bulldozer is shown in the figure). The rotary laser system 1 is fixed on a tripod 3, which is set up at a position as required. A reference plane is formed by a laser beam 4 projected from the rotary laser system 1. A photodetector 5 is fixed on a working tool of the bulldozer 2—for instance, on a mounting pole 7 erected on a blade 6. A distance from a ground surface at the position as required to the reference plane is a known value. If a distance from the reference position of photodetection of the photodetector 5 to the position of a blade edge 6a of the blade 6 is known, it is possible to carry out leveling work as a planned plane when operation for development is performed so that the photodetecting position of the laser beam 4 of the photodetector 5 is maintained at a predetermined position.
FIG. 9 shows the photodetector 5 used on the bulldozer 2.
The photodetector 5 is fixed on the mounting pole 7 by using a pole clamp 8. A photodetection unit 9 is provided on the photodetector 5. The photodetection unit 9 is composed by arranging a multiple of photodetection sensors 11 in a longitudinal direction. Among the photodetection sensors 11, a photodetection sensor 11, which is receiving the light, can be identified by a signal issued from the photodetection sensor 11 receiving the laser beam 4. Based on the position of the photodetection sensor 11, photodetecting position of the laser beam 4 can be detected.
When the ground surface at the working site is flattened or filled with soil according to the reference plane by using the bulldozer 2, ground leveling is often performed on topographical conditions, which are beyond the photodetection range of the photodetection unit 9. It is difficult to detect the light when a photodetector with photodetection range of about several tens of centimeters is used.
Because the blade 6 is moved up and down according to the topographical conditions, the photodetector 5 installed on the blade 6 is not sufficiently operated even when the photodetector 5 has a photodetection unit 9 with no less than a length of 300 mm, for instance. Therefore, to increase the photodetection range of the photodetection unit 9, it is often designed in such manner that the pole 7 can be extended or contracted and the photodetector 5 itself can be moved up and down.
However, a long photodetection unit 9 as described above comprises a multiple of short photodetection sensors 11, and it is disadvantageous because it is very expensive. Further, to move the photodetection unit 9 up and down, a complicated structure including a driving unit and a control unit to control the driving unit, etc. is required, and this means the increase of the cost.
A position measuring system using a photodetection unit with a photodetection sensor having a required length in a vertical direction is disclosed in the Japanese Patent Application Publication No. 11-256620.